Out telescopes aren't sensitive enough to detect the power levels of comm signals that aliens would use internally. Even if SETI saw a random powerful signal that happened to hit us, if the signal doesn't continuously repeat it just gets put into the "random transient, didn't repeat, who knows" bucket, and discarded.
The 100 signals they've detected will be looked at again with telescopes, and when they don't see the same signal repeating, they'll all just be discarded. Even if they were in reality actual emissions from aliens that we happened to see, if they're not intentional, repeating, comm beacons, the signals will just get discarded as unverifiable.
If aliens actually made terrawatt scale comm beacons, we would have easily seen them by now.